(1) Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device that can be formed to have an increased display area relative to a predetermined profile, namely, a so-called narrow frame.
(2) Description of the Related Art
In a liquid crystal display device, there is a TFT substrate in which pixels each having a pixel electrode, a thin film transistor (TFT), and the like are arranged in a matrix form. There is also a counter substrate opposite the TFT substrate, in which color filters, and the like, are formed at positions corresponding to the pixel electrodes of the TFT substrate. Further, a liquid crystal is interposed between the TFT substrate and the counter substrate. Then, the liquid crystal display device forms an image by controlling the transmittance of light for each pixel by the liquid crystal molecules.
The liquid crystal display device is flat and lightweight and its application has expanded in various fields. Small liquid crystal display devices are widely used in mobile phones, digital still cameras (DSC), or other portable devices. There is a strong demand for the small liquid crystal display device to increase the display area while maintaining a small profile. In order to meet this demand, the width from the end portion of the display area to the end portion of the liquid crystal display device is reduced. In other words, it is necessary to make the frame area as a so-called narrow frame.
A sealing material is formed in the frame area to bond the TFT substrate and the counter substrate. Further, an alignment film is formed in the display area of the liquid crystal display device to initially align the liquid crystal. Since the alignment film should completely cover the display area, the area coated with the alignment film should be made larger than the display area by a predetermined width. The alignment process of the alignment film includes a rubbing method and an optical alignment process (hereinafter also referred to as optical alignment). Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-206091) describes a method that achieves: (1) reduce misalignment due to the complex multilayer structure of the pixel portion; and (2) prevent static electricity generated during rubbing, disturbance at the end of the rubbing cloth, and the influence of foreign materials or other contaminants caused by rubbing.
The so-called viewing angle is a problem for the liquid crystal display device. The in-plane switching (IPS) mode controls the amount of light passing through the liquid crystal layer by rotating the liquid crystal molecules in the direction parallel to the substrate, and has excellent characteristics for the viewing angle. At the same time, the IPS mode liquid crystal display device does not require the so-called pretilt angle, and for this reason, is suitable for the optical alignment.
In particular, in the alignment film that has been subjected to an optical alignment process according to a conventional example, the reliability of bonding with the sealing material could be impaired if the alignment film is present between the sealing material and the TFT substrate or between the sealing material and the counter substrate. For this reason, it has been necessary to strictly control the alignment film so that the coating end of the alignment film does not overlap the sealing material.
The alignment film is applied by printing, inkjet, or other printing methods. The alignment film material is liquid which is wet and spread on the surface, and it is difficult to control the coating end of the alignment film. Patent Document 2 (Japanese Patent Application Laid-Open No. 2011-145535) describes a configuration in which a second alignment film is formed in a frame-like shape on the outside of the alignment film formed in the display area, to control the coating region of the alignment film of the display area by the use of the second alignment film as a stopper of the alignment film formed in the display area.
The IPS mode liquid crystal display device has excellent viewing angle and its application has been expanding in various fields. Further, the IPS mode does not require the pretilt angle and is suitable for the optical alignment process. The optical alignment process of the alignment film is a method for irradiating the alignment film with polarized UV light of 300 nm or less, to allow the uniaxial anisotropy to occur in the alignment film. When UV light is irradiated on the alignment film, the polymer that forms the alignment film is separated by the UV light. As a result, the mechanical strength of the alignment film that has been subjected to the optical alignment process is reduced. At the same time, the bonding strength between the sealing material and the alignment film is also reduced.
Thus, in the conventional configuration, the alignment film that has been optically aligned is controlled so as not to overlap the sealing material, or even in the case in which the alignment film and the sealing material have to overlap, the alignment film is formed not to overlap the whole so that a portion of the alignment film does not overlap the sealing material.
FIGS. 14A, 14B, and 14C are views of the configuration when an alignment film 20 and a sealing material 30 do not overlap, in which FIG. 14A is a plan view and FIGS. 14B and 14C are cross-sectional views. FIG. 14A is a perspective plan view. A TFT substrate 100 and a counter substrate 200 are bonded by means of a peripheral sealing material 30. Then, the inside space between the two substrates is filled with a liquid crystal 250. The alignment film 20 is formed so as to cover a display area 10 and to extend to the outside of the display area 10. The sealing material 30 is formed on the outside of the alignment film 20. Note that the alignment film 20 has been subjected to an optical alignment process.
FIG. 14B is a cross-sectional view taken along line A-A of FIG. 14A. In FIG. 14B, the alignment film 20 does not overlap the sealing material 30. FIG. 14C is a cross-sectional view taken along line B-B of FIG. 14A. In FIG. 14C, the alignment film 20 does not overlap the sealing material 30. With this configuration, the bonding strength of the sealing portion is maintained sufficiently high.
However, there is also a type in which the narrower the frame, the more difficult it is to form the outer end portion of the alignment film 20 on the inside of the sealing material 30. FIGS. 15A, 15B, and 15C are views of the configuration in which the width of the frame is reduced in such a way that a portion in the width direction of the sealing material 30, namely, the side of the display area 10 overlaps the alignment film 20. FIG. 15A is a plan view. In FIG. 15A, the display area 10 is formed inside the sealing material 30, in which the inside in the width direction of the sealing material overlaps the alignment film 20.
FIG. 15B is a cross-sectional view taken along line A-A of FIG. 15A. In FIG. 15B, the alignment film 20 overlaps a portion of the sealing material 30. However, the alignment film 20 does not overlap the whole surface of the sealing material 30. In this way, the bonding strength with the sealing material 30 is maintained in the portion in which the alignment film 20 does not overlap the sealing material 30. FIG. 15C is a cross-sectional view taken along line B-B of FIG. 15A. In FIG. 15C, the alignment film 20 overlaps a portion of the sealing material 30. However, the alignment film 20 does not overlap the whole surface of the sealing material 30. In this way, the bonding strength of the sealing material 30 is maintained in the portion in which the alignment film 20 does not overlap the sealing material 30.
However, in order to achieve the configuration shown in FIGS. 14 and 15, it is necessary to accurately control the position of the ends of the four sides of the alignment film 20. Since the alignment film 20 is applied by flexographic printing, inkjet, or other printing methods, the control of the profile is not easy.
An object of the present invention is to achieve a liquid crystal display device in which the profile of the alignment film is easy to control, and at the same time, the reliability of the sealing portion is maintained.